The present invention is directed to a method of fusion pigtailing an optical fiber to an integrated optical device and structures formed thereby.
The term pigtailing generically refers to interfacing an optical fiber with an optical device, e.g., a light source, a detector, a waveguide, etc. Current techniques for securing this interface include bonding, welding, and fusing the optical fiber and the optical device.
In current fusion pigtailing processes, a laser, e.g., a CO.sub.2 laser, is used as a heat source to fuse an optical fiber to a device. This process is sufficient for a small number of ports on a substrate. However, the mechanical strength of the fused joints decreases with increasing chip size.
This decrease in mechanical strength is due to the formation of imperfectly melted joints. The imperfect melting arises when a substrate on which the device is formed has a low thermal conductivity. This low thermal conductivity results in poor diffusion of heat in the depth direction of the substrate. This poor diffusion leads to a large temperature difference between the clad surface layer and the lower part of the core of the fused joint. The mechanical strength may be improved by increasing the power of the laser used for fusing the fiber and the device.
However, since the fiber and the device are being fused together, rather than using another material to secure the interface, power should be kept to the minimal level required for this fusion process. An increase in power also results in an increase in optical loss. This increase in optical loss arises from the higher temperature associated with an increase in power, which may deform the shape of the fiber and/or the device.
Thus, for current fusing methods, if the laser energy is high enough to provide strong fusion, fusion loss is increased. However, if the laser energy is low enough to avoid fusion loss, strong fusion cannot be achieved.
Attempts to create strong fusion without increasing the energy level include providing a heater under the waveguide for preheating or reducing the thickness of the substrate having the waveguide at the interface. However, current solutions involve an interface at which no portion of the substrate is below the fiber. This requires the use of additional elements, such as a fiber carrier, which then must be aligned with and attached to the substrate. Usually, the use of a fiber carrier will also involve using a reinforcing plate.